Sulfonated polymers that include very strong acid groups or salts of the strong acid within a solid matrix have been used in applications as resins or membranes. Generally these sulfonated polymers are random copolymers, where a non-sulfonated homopolymer is converted by a random reaction into the desired sulfonated copolymer. Sulfonated polystyrene (SPS) has been used for more than seventy years and is widely used for ion-exchange resins and as a polymer bound catalyst. Other common sulfonated polymers are sulfonated polyetheretherketones (SPEEK), sulfonated polyphenylenesulfides (SPPS), and sulfonated polysulfones (SPSU). Common sulfonated aliphatic polymers include Nafion and Hypaln, which are perfluorinated and partially chlorinated polymers. Often the randomly placed highly polar functional groups aggregate in one portion of the structure, and remain aggregated in the environments in which they are used.
As the sophistication of applications for polymers evolves, the need for well-defined polymer microstructures ensues. For these applications, the methods of polymer synthesis must extend beyond the random placement of repeating units common to most chain growth copolymerizations of vinyl monomers, condensation copolymerization, or random polymer reactions. Vinyl copolymerizations, even when perfectly alternating, have significant restrictions to the number of covalently bonded carbon atoms between specific functionalized carbons, almost always three carbon atoms. The homopolymerization of functionalized dienes can also lead the structures equivalent to the alternating copolymerization of vinyl monomers but results with separation of functional groups by only five carbon atoms.
Ring-opening polymerizations of specifically functionalized cycloalkene monomers also give limited possibilities to the placement of specific units on the resulting chains as the ability to prepare a cyclic monomer becomes very difficult and usually prohibitively expensive when the size of the ring exceeds seven or eight atoms.
The ring opening metathesis copolymerization, ROMP, for example, of a carboxylic acid functionalized cyclooctene with cyclooctene and subsequent hydrogenation of the double bounds of the polymer formed upon olefin metathesis to yield polyethylene copolymers with between 2-10 mol % acid groups was achieved by the copolymerization and subsequent hydrogenation of an acid functionalized polymer. These materials were isolated as high-melting, semicrystalline solids, as expected, affording strictly linear materials exhibiting varying levels of crystallinity dependent on comonomer incorporation.
The acyclic diene metathesis polymerization, ADMET, of free acid dienes and protected free acid dienes has been reported, for example, in Schwendeman et al. Macromolecules 2004, 37, 4031-37 for ultimate formation of carboxylic acids directly substituted to polyethylene at regular placements and Opper et al. Macromolecules 2009, 42, 4407-9 for ultimate formation of phosphoric acids situated regularly along a polyethylene backbone via a phosphoric ester intermediate.
The preparation of a polyethylene substituted with regularly spaced sulfonic acid groups has not been achieved, even though the preparation of the sulfonic ester equivalent of the phosphoric ester that permitted the formation of the regularly substituted phosphoric acid polyethylene has been achieved. A method to prepare a periodic or quasiperiodic sulfonic acid substituted polyethylene would be of value for proton conducting membranes and other devices where the regularity of substitution can allow specific organization without the uncontrolled acid aggregation common to random copolymer systems.